The present invention relates to the field of semiconductor packaging, and more specifically to a boat for holding land grid array semiconductor packages during assembly.
Conventional land grid array semiconductor packages typically comprise a matrix of electronically conductive pads disposed on a substrate surface for coupling between the substrate and a semiconductor chip, printed circuit board or other components. The conductive pads are commonly gold or nickel plated and may be distributed over all or part of the substrate surface, up to the outer edges.
In order to increase package production throughput and efficiency, conventional carrying devices, such as trays or boats, are typically employed to hold semiconductor packages during and between various assembly steps. Individual semiconductor packages are held in pockets cut out of the carrying device.
In accordance with conventional packaging techniques, land grid array packages are held during assembly in carrying device pockets designed to support each package via the package""s outer edges. For many semiconductor package types, such as pin grid array packages, this approach is acceptable either because the surface attachments are located on the semiconductor package in a manner that keeps the semiconductor package edges free or because the semiconductor package does not have surface attachments.
The surface of land grid array packages, however, differs in that the entire surface may be populated with metal-plated conductive pads. As a result, there is often insufficient distance between the outermost conductive pads and the edge of the land grid array package to support them by their outer edges in a conventional carrying device pocket without causing the rows of conductive pads closest to the four outer edges of the land grid array package surface to come into contact with the carrying device. Such contact with the carrying device is problematic because it causes contamination and/or damage as by scratching of the conductive pads, thereby adversely impacting device performance. For example, impressions in the conductive pads result in solder voids; as when solder balls or other parts are attached, that impede mechanical or electrical functions.
Another problem frequently encountered upon employing conventional carrying devices to accommodate land grid array packages stems from the fact that land grid array packages are light in weight. As land grid array packages pass through the assembly process, the carrying devices holding these packages are subject to movement that can cause a land grid array package to bounce or jump in the carrying device pocket. The conventional carrying devices currently employed to support land grid array packages have relatively shallow holding pockets and no containment feature, such as a lid. This carrying device design feature, combined with the land grid array package""s light weight, create an unstable situation such that even minimal carrying device movement results in ejection or discharge of a land grid array package completely out of the carrying device or unseating of the land grid array package so that it sits askew in the carrying device pocket Land grid array package manufacturers, therefore, experience reduced yield rates and increased rework stemming from conventional carrying device-related damage.
Conventional carrying device pockets are not designed to address package size variations, thereby exacerbating damage and package jumping. For example, conventional land grid array packages are manufactured in a variety of dimensions, as known in the art. In situations wherein the carrying device pocket is larger than the land grid array package, the likelihood that the package will slide around within the pocket is increased, thereby rendering more conductive pads than just those in the outermost rows of the land grid array package vulnerable to contact with the carrying device and damage.
The larger carrying device pocket size is also conducive to package jumping and damage. The pockets in conventional carrying devices typically have sharp edges around the top and bottom pocket openings and support shelf areas. These sharp edges can scratch or otherwise damage semiconductor packages if the packages are not carefully placed in the pocket. Land grid array packages present special concerns because their weight makes them susceptible to being dislodged from conventional carrying devices during handling, even when the carrying device pocket size is appropriate. When the carrying device pocket is oversized with respect to the land grid array package, jumping becomes even more likely, thus exposing the land grid array package to contact with the sharp edges of the pocket. In addition to exposing the conductive pads and other package parts to scratching and denting, excess movement and jumping can be especially damaging to ceramic land grid array packages that are prone to breaking when they strike other hard objects, like a carrying device.
There is a need for a carrying device that can hold land grid array packages in place during assembly without contaminating, scratching, denting or otherwise damaging the conductive pads or other parts on the land grid array package or the land grid array package itself.
The present invention addresses and solves the above-mentioned problems attendant upon accommodating land grid array packages during assembly by providing a boat comprising a plurality of layers with aligned through-holes. The through-holes in each layer are strategically designed to provide secure, safe accommodation for a land grid array semiconductor package. Embodiments of the present invention comprise a boat having a bottom layer with an array of through-holes having a substantially square cross-sectional shape with rounded corners, a middle layer with an array of through-holes having a substantially octagonal cross-sectional shape and a top layer having an array of through-holes having a substantially square cross-sectional shape with notched sides. Vertical tabs extend upward from the sidewalls of each notched side. The cross-sectional area of each middle layer through-hole is larger than the cross-sectional area of each bottom layer through-hole and the cross-sectional area of each top layer through-hole is larger than the cross-sectional area of each middle layer through-hole. The through-holes in the bottom layer, middle layer and top layer each have a central axis. Each middle layer through-hole central axis is substantially aligned with the central axis of a corresponding bottom layer through-hole. Each top layer through-hole central axis is substantially aligned with the central axis of a corresponding middle layer through-hole. The middle layer is attached to the bottom layer so that the middle layer through-holes are substantially aligned over the bottom layer through-holes, thus forming octagonal frames around the bottom layer through-holes exposing a resting area comprising a portion of the bottom layer""s upper surface. The top layer is attached to the middle layer so that the top layer through-holes are substantially aligned over the middle layer through-holes, thus exposing four corner supports on the upper surface of the middle layer. The layers may be attached by spot welding or other means.
The present invention advantageously eliminates contact between the boat and critical land grid array package conductive pads, thereby improving the quality of the land grid array flip chip packages assembled using the present invention by reducing instances of damage to such conductive pads. Boats in accordance with embodiments of the present invention also accommodate a variety of land grid array package sizes, thereby advantageously improving production speed and reducing production costs by eliminating the need for multiple boats of varying design to complete package assembly.
Boats in accordance with embodiments of the present invention effectively retain land grid array packages in place during movement through the assembly process, advantageously reducing damage due to boat dislodgment, or improper seating, such as scratching or contamination. The present invention also enables superior alignment between land grid array packages and assembly equipment during component placement, thereby increasing accuracy in land grid array package production and increasing output quality.
Other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description. The embodiment shown and described provides illustration of the best mode contemplated for carrying out the invention. The invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings are to be regarded as illustrative in nature, and not as restrictive.